1. Field of the Invention
The present invention relates to a battery charging apparatus for supplying electric energy to the battery of a battery-powered electric vehicle through a receiving coupler mounted on the electric vehicle.
2. Description of the Related Art
Recent years have seen progress in the development of electric vehicles as means of transportation for reducing the rate of consumption of existing fossil fuels and avoiding possible environmental pollution. Electric vehicles are powered by electric energy stored in and supplied from batteries mounted thereon. The battery on an electric vehicle needs to be charged with electric energy from an external source from time to time. For supplying electric energy to the battery, the electric vehicle has a receiving coupler that can be fitted over an energy supplying coupler of an electric energy supply station.
If, when the electric vehicle is moved to the electric energy supply station, the energy supplying coupler can automatically engage the receiving coupler and start automatically charging the battery through the receiving coupler, then the burden on attendants at the electric energy supply station can be minimized.
One battery charging apparatus which is capable of such automatic battery charging operation is disclosed in Japanese laid-open patent publication No. 6-14408, for example. According to the disclosed battery charging apparatus, the two-dimensional position and attitude of an electric vehicle with respect to a battery charging apparatus are detected by a position detector, and the feeding coupler of the battery charging apparatus is displaced on the basis of the detected two-dimensional position and attitude, so that the feeding coupler can be connected to the receiving coupler.
Japanese laid-open patent publication No. 9-182212 discloses another battery charging apparatus which has a position detector disposed so as to face the front side of an electric vehicle, for detecting a lateral position of the electric vehicle. The feeding coupler of the battery charging apparatus is displaced on the basis of the detected position, so that the feeding coupler can be connected to the receiving coupler.
According to the above conventional battery charging apparatus, however, since the coupling accuracy with which the feeding coupler is connected to the receiving coupler depends on only the position detector of the battery charging apparatus, if the coupling accuracy is to be increased, then not only the positional detector needs to be highly accurate, but also the feeding coupler has to be displaced by a highly accurate mechanism. As a consequence, the conventional battery charging apparatus are necessarily highly expensive to manufacture.
Furthermore, because the couplers would tend to be damaged if the electric vehicle happened to move while the battery is being charged, it is necessary for the conventional battery charging apparatus to perform a control process for detecting the position and attitude of the electric vehicle at all times during the charging of the battery, and effecting positional correction of the electric vehicle. Such a control process may be dispensed with by making the feeding coupler angularly movable to accommodate accidental movement of the electric vehicle. However, when the feeding coupler swings in the process of being coupled to the receiving coupler, the feeding coupler and the receiving coupler may not be able to achieve a desired exact coupling therebetween, and may possibly be damaged.